The goals of the research proposed herein are to study the mechanisms by which intracellular pH (pHi) is regulated in type II alveolar epithelial cells, and to investigate the effects of pHi on the functional and biological properties of alveolar epithelium. Intracellular pH is an important biological parameter in all living cells whose regulation is necessary for normal cellular homeostasis. pHi, and the ion transport mechanisms by which it is regulated, may contribute to many important cellular processes, including transcellular transport, cell volume and osmolarity regulation, and cellular electrolyte composition. In addition, changes in pHi may serve as intracellular signals for biological processes such as cell growth and differentiation. Therefore, (1) we will identify and characterize the ion transport processes responsible for pHi regulation in granular pneumocytes, including determination of their distribution with respect to membrane polarity. We will perform this work primarily on rat type II alveolar pneumocytes in primary culture on tissue culture treated porous and nonporous supports. Several techniques will be utilized to identify and characterize these processes, including spectrofluorometry, radioisotope uptake methods and antibody binding studies. (2) We will examine the effects of extracellular stimuli (e.g., hormones and growth factors) on pHi regulation in type II alveolar epithelial cells utilizing these techniques. (3) We will investigate the effects of pHi on several aspects of function and biology of alveolar pneumocytes, including regulation of extracellular alveolar fluid pH, epithelial barrier properties, and growth and morphology of alveolar epithelium in vitro. Many of the critical issues in current pulmonary research involve processes that pHi is most likely to affect, including maintenance of alveolar epithelial barrier integrity, development of epithelial polarity, epithelial proliferation and differentiation, and regulation of transepithelial transport with respect to alveolar fluid and solute balance in normals and in individuals with excess alveolar fluid (i.e., pulmonary edema). It is our premise that investigations into the regulation of intracellular pH in alveolar pneumocytes, and the regulatory effects of pHi in turn on other cellular processes, are likely to yield information important to the study of lung biology and pulmonary disease.